This invention relates to a process for producing a particulate fuel from coal having a reduced water content while economically using process water that is produced during processing. The fuel can be dried subbituminous coal or a pyrolyzed coal, also known as char or pyrolyzed carbonaceous materials. Hereinafter, the term char shall apply to ambient and dried coal, the really dried coal, or pyrolyzed coal, or other appropriate carbonaceous material.
Many of the coal deposits in the United States that are easily mined are referred to as low rank coals, i.e., coals that contain a considerable quantity of inherent moisture (ASTM D 121-73) and have relatively low specific heating values. These coals are desirable as fuels, but the cost of transporting them to coal burning facilities is high due to their water content. The high water content also lowers the efficiency of the coal burning facility since the water has to be evaporated in the conversion to thermal energy. While these coals are expensive to transport long distances, many are very desirable because they have relatively low sulfur contents and may not require extensive equipment for removing sulfur from the stack gases when they are burned. In addition, the coals normally are inexpensive to mine by surface procedures since they are located relatively near the surface of the earth, especially in the Western states.
The Western low rank coals typically contain 20-40 perent water by weight and have a heating value of approximately 7000-9000 BTU per pound. In contrast, if the coal's typical water content can be lowered to 4 to 7 percent by weight, then the heating value of 8000 Btu/lb, 30% water by weight coal can be increased to 12,000 BTU per pound, or more by the appropriate processing. From these figures, it can be seen that the value of the coal can be increased substantially if an economical process can be developed for removing the water from the coal. In addition to removing the water from the coal, the process also must provide for the use or disposal of any water generated by the process i.e. process water. This process water can contain substances which make it difficult to dispose of the water in conventional watersheds. When a coal's temperature is raised to temperatures in excess of about 600.degree. F., some hydrocarbons are driven off the coal, which include phenols and water soluble hydrocarbons. The process water contains these hydrocarbons. These products obviously must be removed from the process water before the process water can be disposed of in conventional watersheds or released into the atmosphere. Alternatively, the water can be used in the process as described below.